Food warming appliance

ABSTRACT

A food warming appliance having base and cover structures defining a portable case. A pair of opposed heating panels are mounted, one on each of the structures, and biased toward each other so as to firmly engage food positioned therebetween when the structures are closed. Foods and food trays of a wide variety of sizes, shapes and thicknesses can be positioned between the panels and firmly gripped so as to be warmed through a gentle conductive heat transfer. The heating compartment is well insulated and has the capability of serving as a cold food storage area to keep frozen foods frozen for substantial periods of time. A safety electrical interlock system normally deenergizes the heating panels when the appliance is open. An interlock by-pass plug and cord permit open case operation where the appliance is to be used to keep foods warm during serving. A supporting rack structure is provided for receiving and energizing a plurality of such appliances. Selection switches permit selection of one of several predetermined food serving times. Methods of warming foods for consumption by an individual or large numbers of people through use of such appliances and supporting rack structures are described.

United States Patent 1191 Frey et al.

[451 July 17, 1973 1 1 FOOD WARMING APPLIANCE [76] Inventors: IrwinKenneth Frey, PO. Box 4836, Fairview Park, Ohio 44126; Charles L. Zola,24619 Royalton Road, Columbia Station, Ohio 44028 [22] Filed: July 18,1972 [21] Appl. No.: 273,013

[52] US. Cl. 219/387, 99/391, 219/404, 219/456, '219/521, 219/525 [51]Int. Cl. F27d 11/02 [58] Field of Search 219/386, 387, 521, 219/403,404, 439, 444, 456, 447, 524, 525; 99/171, 391

[56] References Cited UNITED STATES PATENTS 2,993,431 7/1961 Weishaus99/391 3,440,406 4/1969 Sego, .lr. 219/456 X 3,385,952 5/1968 Mix219/387 2,990,286 7/1961 Clarke et a] 99/171 3,548,154 12/1970Christiansson 219/403 3,610,884 10/1971 Evans et al. 219/439 3,632,982l/1972 Linger 219/447 3,678,248 7/1972 Tricault et al, 219/525 PrimaryExaminerVolodymyr Y. Mayewsky Attorney-David A. Burge et al.

[57] ABSTRACT A food warming appliance having base and cover structuresdefining a portable case. A pair of opposed heating panels are mounted,one on each of the structures, and biased toward each other so as tofirmly engage food positioned therebetween when the structures areclosed. Foods and food trays of a wide variety of sizes, shapes andthicknesses can be positioned between the panels and firmly gripped soas to be warmed through a gentle conductive heat transfer. The heatingcompartment is well insulated and has the capability of serving as acold food storage area to keep frozen foods frozen for substantialperiods of time. A safety electrical interlock system normallyde-energizes the heating panels when the appliance is open. An interlockbypass plug and cord permit open case operation where the appliance isto be used to keep foods warm during serving.

A supporting rack structure is provided for receiving and energizing aplurality of such appliances. Selection switches permit selection of oneof several predetermined food serving times. Methods of warming foodsfor consumption by an individual or large numbers of people through useof such appliances and supporting rack structures are described.

14 Claims, 14 Drawing Figures iii? Patented fJ ul yv17,-1973 4Sheets-Sheet X Patented July 17,.1973

4 Sheets-Sheet :5

FOOD WARMING APPLIANCE BACKGROUND OF THE INVENTION 1. Field of theInvention The present invention relates generally to a portable foodwarming appliance and methods employing such appliances for heatingfoods for consumption by an individual or large numbers of people.

2. Prior Art Many proposals have been made for incorporating foodwarming devices into portable containers, such as lunch boxes and thelike, for transport together with prepared food and such utensils as arerequired to serve and consume the food. Proposals have also been made inan effort to provide portable lunch kits specially adapted to receive,transport, and heat frozen food trays. One such proposal is set forth inU.S. Pat. No. 3,385,952, issued May 28, 1968 to E. W. Mix.

A significant disadvantage of known portable food warming devices is theinefficiency with which they heat food. Portable food warmers to datehave principally relied on the heating techniques of convection andradiation to warm the food. Typically one or more heating devices isdisposed in spaced relationship with the food to be warmed. While anumber of proposed food warmers dispose the heating element within achamber which also holds the food to be warmed, most dispose the heatingelement outside the chamber. In either arrangement, the resulting systemis in essence a small oven providing a heating compartment which issubstantially larger than the food positioned therein for warming. Verylittle use has been made in known portable food warmers of the moreefficient heating technique of conduction as opposed to radiation andconvection.

Radiation and convection heating techniques are not only less efficientand consequently more costly than is conduction heating, but theyfurther necessitate the heating of one or more heating elements to atemperature which is higher than that needed for conduction heating. Toexpress this problem in another way, radiation and convection techniquesrequire more time to transfer a given quantum of heat to the food thandoes conduction heating, assuming the heating elements in bothsituations are at the same temperature. Accordingly, in order to warmthe food within a reasonable period of time by radiation and convectiontechniques, the heating element temperature is ordinarily elevatedconsiderably above the temperature to which the food is to be heated. I

High temperature heating element operation, in and of itself, createsseveral problems. First, the food warmer components must be constructedto withstand the high heating element temperatures. This oftennecessitates the use of special heat resistant materials therebyincreasing the cost of the food warmer. Second, where high heatingelement temperatures are involved, substantial amounts of heatinsulating materials must be provided to keep the exterior portions ofthe food warmer case cool.

Still other problems due to high heating element temperatures areencountered with respect to the warming function of the apparatus inthat the foods being warmed often tend to scorch and dry out. The foodportions nearest the heating element tend to reach tem peratures abovethetemperature to which the food is to be warmed while interior portionsof the foods are still below the desired temperature. Consequently,depending on the type of food being warmed, various adverse surfaceeffects are encountered. The surfaces of some foods tend to cook ratherthan to warm. This changes the character of the food being warmed in anundesirable fashion. The surfaces of other foods tend to dry out so asto become undesirably crusty. Other foods tend to scorch or burn givingthem a very unpalatable appearance and flavor.

Most known food warming devices cannot be used to keep food warm andready to serve for a prolonged period of time without adverselyaffecting the food. This disadvantage is particularly annoying where theoperator has energized the food warmer in anticipation of consuming thefood at a predetermined future time, and is then delayed unexpectedlywhereupon the food becomes overheated and cooks, scorches, dries out,

burns or otherwise loses its appetizing appeal. It is not uncommon thatthe food is rendered entirely inedible where it is left in the heatedapparatus substantially longer than anticipated.

There are many industries where large shifts of employees are givenbrief lunch breaks that begin and end at set periods. While it isdesirable to provide each employee with a warm lunch, significantproblems and expenses are encountered in maintaining and operatingcafeterias of sufficient size to accommodate large numbers'of employeesin short time intervals. Moreover, a number of employees find they canbring food from home on a daily basis at a lesser cost than is involvedin cafeteria dining. Still other employees are faced with specialdietary requirements that cannot be provided for in the cafeteria menu.

In other industries, for instance construction work, there are nocafeterias or other facilities where the employee can readily purchase awarm lunch. In these employments, it is common for the workers to carrytheir lunches daily from home. If the employee wants part or all of hislunch warm at his lunch break, the usual approach is to pre-heat thefood at home and pack it in insulated containers. While the insulatedcontainers have been remarkably improved in recent years, the factremains that they do nothing in and of themselves to further heat thefood, and the food accordingly gradually cools'off. Moreover, many foodsdeteriorate if kept at elevated temperatures for several consecutivehours. Accordingly, the types .of foods which can be kept warm aresubstantially limited in number.

Accordingly, while it is recognized as being desirable to provideemployees with facilities which will enable them to daily enjoy a warmlunch including food of their choice at a minimum of expense to theemployee, the fact remains that there is no way to providecafeteria-style facilities for employees in many industries, and wherecafeterias are provided they still do not serve the needs of someemployees.

While many portable lunch kits with self contained heating units andcontrol timers have been proposed as a possible solution to the workmansneed for a warm lunch, the fact remains that the proposed lunch kitshave had too many problems associated therewith to gain any substantialacceptance.

SUMMARY OF THE INVENTION The present invention overcomes the foregoingdrawbacks of prior art food warming devices and provides novel andimproved methods and apparatus for heating foods and providing heatedfoods for consump tion by one or even a large number of people.

In accordance with the present invention, food to be warmed isconductively heated by means of a pair of opposed heating panels whichfirmly engage opposite sides of the food. Such an arrangement is to bedistinguished from an oven-type heating appliance which disposes thefood in a compartment of significantly greater size than the food to beheated with the heating element in spaced relationship to the food, andthen heats or warms the food principally by radiation and/or convection.

Whereas radiation and convection heating techniques tend to result in anoverheating of the food surfaces most directly exposed thereto, theconduction heating system of the present invention does not have thiseffect. The heating elements reach a temperature which is notappreciably above the temperature to which the food is to be warmed.Accordingly, the food surfaces in contact with the heating elements arenot heated to unduly high temperatures, and the food is heated gently.

It has been found that the conductive heating arrangement of the presentinvention serves to direct the heat from the heating elements into thefood so as to minimize heat transfer to other portions of the apparatus.Moreover, the arrangement of the present invention results in a deliveryof maximum heat to the coldest areas of the food so as to warm the foodsubstantially uniformly. These are important advantages which deservefurther explanation.

Heat tends to radiate uniformly in all directions from a heatingelement. Accordingly, in radiation/convection heating devices, asubstantially amount of heat is transferred to the appliance itselfthereby requiring a substantial amount of insulation and requiring theuse of materials which will withstand high temperatures. The portion ofthe radiated heat which is delivered to the food tends to heat thesurface of the food relatively quickly to relatively high temperaturesbefore the heat can be dissipated in the food by conduction.

The present invention not only minimizes heat loss to the appliancestructure which surrounds and mounts the heating elements, but alsoovercomes the problem or temperature build-up on the food surfaces so asto effect a delivery of maximum heat to the coldest areas of the food.The transfer of heat by conduction results in the largest heat flowbetween areas of greatest temperature differential. Accordingly, (I)where the food is colder than the surrounding portions of the appliancewhich mount the heater elements, the maximum heat flow will be directedinto the food and not into other portions of the appliance; and (2)since the food is in intimate contact with the heating elements,conductive heat transfer will proceed at a maximum rate between thehottest regions of the heating elements and the coldest regions of thefood. By this arrangement, the food surfaces do not become overheatedwhile the regions inwardly of the food remain frozen. Rather, the foodtends to warm in a substantially uniform fashion.

In an apparatus constructed in accordance with the present invention,the food is securely engaged or clamped on two opposite sides ofrelatively large crosssectional areas. Accordingly, a large heat inputarea is utilized in transferring heat from the heating elements to thefood. Since a large heat input area is utilized, a small heat input persquare inch will result in a large total heat input. Moreover, theheating compartment is essentially confined to the size of the foodbeing heated such that minimal radiation and convection heat losses areincurred. These several features combine to give a very gentle andhighly efficient heating action.

The efficiency of operation of the present invention cannot be overemphasized. By virtue of the direct conductive heating arrangement, onlyabout 300-400 watts power input are required to warm a typical foodserving. A frozen dinner can be thawed and warmed in approximately 20-30minutes, which is at least comparable to, if not less than, the timeneeded to perform the same function in the 240 volt oven of an ordinarykitchen range. The 300-400 watt input requirement of the presentapparatus is even substantially less than that of the ordinary householdcoffee pot which typically consumes about l,000 watts at the start ofits operation. Accordingly, the cost of operating the apparatus of thepresent invention is quite low.

The low energy input requirement renders the apparatus of the presentinvention much more nearly usable in automotive and boat applicationsthan prior art food warming systems. Particularly where longer foodwarming times are tolerable, the energy requirement of the heaters canbe considerably reduced so as to render possible operation from boat andautomotive ignition systems.

Still another feature of the low power input requirement is improvedoperator safety. The various components of the apparatus are heated torelatively low temperatures and are so insulated that the likelihood ofoccasioning burns is very small.

Turning now more specifically to other structural features of theapparatus, the mounting of the heating panels is of particular interest.In the preferred embodiment both the upper and the lower panels aremounted in a floating fashion and biased toward each other. Among theadvantages of this arrangement are:

l. The apparatus is not limited to use with food containers of anyparticular size or configuration. The apparatus will not onlyaccommodate food containers of a wide range of thicknesses, but also awide range of sizes and shapes.

2. Regardless of the shape or size of the food container placed betweenthe heating panels, it will be held firmly in place so as to not bounceabout or open accidentally.

3. The apparatus is not limited to use with preformed food containers.Food which is not wrapped at all or simply wrapped in metallic foil canbe warmed.

The floating mounting of the heating panels is provided by disposingeach panel within a pan and interposing compression coil springs betweeneach heating panel and its surrounding pan so as-to bias the heatingpanels toward the rims of the pans. Stops are provided adjacent the panrims to limit the travel of the heating panels. 1

By arranging the stops in the form of projections which engage theheating panels along two opposite edges, the heating panels can beremoved simply by depressing one edge so as to cock the panel in its panthereby permitting the opposite edge to be elevated out of the pan pastits stop projections. Accordingly, should any liquid seep into theregions of the pans behind the heating panels, the panels can be removedto facilitate cleaning.

Silicone rubber sealing rings are positioned around the rims of the pansso that when the base and cover of the appliance are closed, the sealingrings engage each other to prevent liquid seepage into other areas ofthe appliance. Sealing rings are also interposed between the edges ofthe heating panels and the interior walls of the pans to prevent liquidseepage into the regions behind the heating panels. Moreover, thesealing rings additionally serve to insulate the heater panels from thepans, and the pans from their supporting structure.

The food heating compartment is well insulated from the outer case bothby the provision of insulating mate rials therebetween and by virtue ofthe mounting of the heating panels so as to establish a poor heatconducting path to adjacent components. This insulated feature not onlyincreases the efficiency of operation of the appliance during heating,but also gives the appliance a cold storage capability that enables itto keep frozen dinners frozen for substantial periods of time prior tothe initiation of the heating cycle.

An electrical interlock safety feature is provided which will ordinarilyserve to de-energize both heating panels once the base and cover areopened. Where it is desired to use the heating panels in open-caseoperation to keep dishes of food warm during serving, two means areprovided for overcoming the operation of the interlock. Where only oneheating panel is needed for open-case operation, a plug is providedwhich can be inserted into the interlock component of the base to permitoperation of the base-carried heating panel.

Where both heating panels are required for open-case operation, aninterlock by-pass cord is provided to electrically interconnect theinterlock components of the base and cover.

The apparatus of the present invention can be used to warm a widevariety of foods. While it is well suited for use in thawing and heatingtrays of frozen food, it is not limited to use with frozen food. Aparticularly delicious meal can be prepared by warming a pre-cookedsteak and mushrooms wrapped together in aluminum foil. The low gentleheat can be used to cook delicate fish or to heat hot dogs or to meltcheese or chocolate. Sandwiches can be warmed without being wrapped ifdesired. Many other uses will be apparent.

, In order to permit large scale use of such appliances by factoryworkers, construction workers and other working people, a rack structureis provided which will receive and energize a plurality of food warmingappliances. A separate compartment is provided for each food warmingappliance. At the rear of each compartment is an electrical plug whichwill register with an appliance carried plug when the appliance ispushed fully inwardly of a compartment. A separate selector switch isprovided to selectively connect the appliance to one of a plurality ofmaster timers. By this arrangement, a workman can select one of severaltimes when his lunch is to be ready.

Such rack structures can be located in convenient areas of industrialplants or can be made in the form of mobile units for use atconstruction sites. If the rack structures are to be positioned in adusty environment, the compartments can be provided with separatewindowed doors. Moreover, individual keyed locks can be incorporated inthe doors in the fashion of baggage lockers so that each workman cansecure his food warming appliance and have no fear that it will beunplugged or the selected serving time changed.

In view of the foregoing summary, it should be apparent that the foodwarming appliance of the present invention is a highly versatile devicecapable of warming most foods so that they taste better than foodswarmed in oven-type enclosures, capable of highly efficient, low-costoperation, and adapted for individual home use, boat and automotive use,and particularly to large scale use in industrial plants, atconstruction sites and the like.

Accordingly, it is a general object of the present invention to providea novel. and improved conductive heating portable food warmingappliance.

It is another object to provide such an appliance which is adapted toreceive and warm foods and food trays of a wide variety of shapes, sizesand thicknesses.

It is still another object to provide a means and method employing suchappliances for warming foods for consumption by large numbers of people.

Other objects and a fuller understanding of the invention may be had byreferring to the following description and claims taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of thefood warmer of the present invention with the case closed and in anupright position for transport;

FIG. 2 is a perspective view of the food warmer with the case open toillustrate the interior construction;

FIG. 3 is a perspective view of the food warmer with the case closed andpositioned in the horizontal operational position and with power forheating being supplied through an auxiliary power cord;

FIG. 4 is an enlarged sectional elevational view of the food warmer inclosed position, the base and cover structures being spaced apart in thedrawing to more clearly illustrate the details of construction;

FIG. 5 is a sectional elevational view on an even more enlarged scale ofa portion of the food warmer particularly illustrating the mounting oftheheating panels;

FIG. 6 is a schematic diagram illustrating how the heating panels can becocked slightly for removal;

FIG. 7 is a schematic illustration of the electrical circuitry includinga safety interlock;

FIG. 8 is a perspective view of the base of the appliance as providedwith an interlock over-ride plug for open-case food warming operation;

FIG. 9 is a schematic illustration of the electrical wiring arrangementof the interlock over-ride plug shown in FIG. 8;

FIG. 10 is a perspective view of the appliance with the base and coverstructures separated for open-case operation and interconnected by aninterlock by-pass cord;

FIG. 11 is a schematic illustration of the electrical wiring arrangementof the interlock by-pass cord shown in FIG. 10;

FIG. 12 is a front elevational view of a rack structure for receivingand energizing a plurality of food warming appliances;

FIG. 13 is an enlarged cross-sectional view as seen from the planeindicated by the line l313 in FIG. 12; and,

FIG. 14 is a cross-sectional view on an even more greatly enlarged scaleof the electrical interconnection between a food warming appliance andthe supporting rack, as seen from the plane indicated by the line 14-14in FIG. 13.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIGS. l-3, aportable electric food warming appliance constructed in accordance withone aspect of the present invention is shown generally at 10. A matingbase 11 and cover 12 cooperate to define a portable housing or casewithin which the heating components of the food warmer are mounted fortransport and operation. Opposed electrically energized heating panels13, 14 are mounted within the base 11 and cover 12 in a floating fashionas will be described in greater detail.

With the base 11 and cover 12 open as shown in FIG. 2, food to be warmedsuch as a sandwich wrapped in aluminum foil or a tray of frozen food, ispositioned on the heating panel 13. The cover 12 is then closed so as toclamp the food between the heating panels l3, 14. Since the base 11 andcover 12 are well insulated, as will be explained, the food will be keptat approximately its original temperature for periods of reasonablelength such as 4-5 hours. During this time, the appliance 10 can beuprighted to the position of FIG. 1 for transport. The food warmingoperation is carried out with the appliance in the generally horizontalposition of FIG. 3. As shown in FIG. 3, an auxiliary power cord 15 isprovided for energizing the appliance 10 by means of a standardwall-mounted electrical outlet 16. By virtue of the fact that the foodto be warmed is clamped between the heating panels 13, 14, the warmingof the food is carried out primarily through the direct heatingtechnique of conduction as opposed to the techniques of radiation andconvection. This heating arrangement is advantageous in many respects,several of which will be described.

The base 11 and cover 12 are molded to define mating pan-like structuresincluding generally planar outer walls 21, 22. Formed integrally withthe outer wall 21 of the base 11 are back and front walls 23, 25 andopposed sidewalls 27, 29. Formed integrally with the outer wall 22 ofthe cover 12 are back and front walls 24, 26 and opposed sidewalls 28,30.

In a conventional fashion, hinges 31, 32 pivotally interconnect the base11 and'cover 12 along the back walls 23, 24. Cooperating latch lockcomponents 33, 34 of conventional design are mounted on the front walls25, 26 to releasably hold the base 11 and cover 12 in closedconfiguration. A carrying handle 35 is pivotally mounted on the base 11to facilitate transporting the appliance.

The interior of the appliance case is partitioned into separate heatingand utility compartments. Partitions 41, 42 and 43, 44 divide the base11 and cover 12 into mating utility compartments 45, 46 and 47, 48. Theremaining interior regions of the base 11 and cover 12 house the heatingpanels l3, 14 as will be described.

The mating utility compartments 45, 46 are provided for housing thepower supply cord 15 and an interlock by-pass cord 50 which will bedescribed. A pair of cooperating female and male electrical interlockcomponents 51, 52 are mounted within the compartments 45, 46. As willalso be described, the interlock components 5], 52 serve to preventenergization of the heating panels 13, 14 when the base 11 and cover 12are opened. The interlock by-pass cord 50 is designed to overcome theoperation of the interlock components 51, 52 during specialcircumstances where it is desirable to energize the heating panels 13,14 with the base 11 and cover 12 open.

The mating utility compartments 47, 48 are provided for housing suchutensils as are required to serve and consume the food warmed by theappliance 10. By way of illustration, a fork 55 and spoon 56 are shownpositioned in the compartment 47.

Referring to FIGS. 4 and 5, a pair of metallic pans 61, 62 arepositioned interiorally of and in spaced relationship to the base 11 andcover 12. The pans 61, 62 define a pair of mating recesses within whichthe heating panels 13, 14 are mounted. As will be explained in greaterdetail, the heating panels 13, 14 are biased toward each other so as toclamp the food to be heated therebetween. The heating panels l3, 14 arealso re movable in order to clean the pans 61, 62.

The pans 61, 62 are mounted in an insulated fashion in the base 11 andcover 12. The region between the pan 61 and the base 11 is filled with afiberglass insulation layer 63. The region between the pan 62 and thecover 12 is similarly filled with a fiberglass insulation layer 64.Disposed around the rims of the pans 61, 62 are silicone rubber strips65, 66 which insulate the pans 61, 62 from supporting frame structures71, 72.

In addition to insulating the pans 61, 62 from the frame structures 71,72 the silicone rubber strips 65, 66 serve the secondary function ofproviding a peripheral seal around the pans 61, 62 which prevents theseepage of liquids from the region of the pans through other portions ofthe appliance. The silicone rubber strips 65, 66 are clamped by means ofrivets 67, 68 between the frame structures 71, 72 and the pans 61, 62.This prevents the seepage of liquids between the pans 61, 62 and theframe structures 71, 72. Moreover, the strips 65, 66 extend above therim of the pan 61 and below the rim of the pan 62 so as to be clampedtogether when the base 11 and cover 12 are closed. This prevents theseepage of liquids between the strips 65, 66 when the appliance isclosed.

The frame structures 71, 72 include trough-like deck members 73, 74which surround the rims of the pans 61, 62 and bridge the space betweenthe pans 61, 62 and the base 11 and cover 12. Rivets 75, 76 rigidlysecure the deck members 73, 74 to the base 11 and cover 12. The rivets67, 68 extend through the silicone rubber strips 65, 66 and serve tosupport the pans 61, 62 rigidly from the deck members 73, 74.

The heating panels 13, 14 each comprise a flat bonded assembly of a thinaluminum facing plate 80, a heating element 81, and an insulating sheet82 of asbestos laminate. The heating elements 81 are preferably siliconrubber laminated electrical resistance heating devices of the type soldunder the trademark WAT- TLOW by the Ogden Company of St. Louis,Mo.These heating elements 81 are available with a thermostat hermeticallysealed therein so that the temperature of the heating elements 81 can bepre-set and accurately regulated. Preferably the heating elements 81include such a thermostat which is pre-set for a temperature limit ofapproximately 200F.

The aluminum facing plates of the heating panels 13, 14 extend beyondthe edges of the heating elements 81. Silicon rubber sealing rings 83are peripherally supported on the facing plates 80. The sealing rings 83serve to insulate the facing plates 80 from the pans 61,

62 while simultaneously providing a seal therebetween which preventsliquid seepage into the regions beneath the heating panel 13 and abovethe heating panel 14.

A significant feature of the present invention resides in the provisionof a floating" mounting for the heat ing panels 13, 14. Referring toFIG. 5, interposed between the panels 13, 14 and the pans 61, 62 are aplurality of compression coil springs 85. The ends of the springs havesilicon rubber feet 86 compressed thereover so as to be held firmly onthe springs 85. THe feet 86 provide a resilient cushion between thesprings 85 and the panels 13, 14 and pans 61, 62 which assists inholding the springs in place and deading any noise which would otherwise result during relative movement of these members. Moreover, thefeet 86 serve as insulators to prevent conductive heat transfer from thepanels 13, 14 through the springs 85 to the pans 61, 62. Indentations 87are provided in the pans 61 62 to facilitate positioning of the springs85 during assembly.

The springs 85 serve to bias the panels 13, 14 toward each other. Thenormal upward movement of the lower panel 13, and the downward movementof the upper panel 14 are limited by engagement of the sealing rings 83with the inner ends of the rivets 67, 68. By this arrangement, therivets 67, 68 serve the function of stops which hold the heating panels13, 14 in the base 11 and cover 12 when no food is positioned betweenthe panels 13, 14.

The rivets 67, 68 having inwardly projecting ends which serve as stopsfor the panels 13, 14 are preferably located only along opposite ends ofthe panels 13, 14. This arrangement enables each of the heating panelsto readily be removed simply by depressing one end of the panel and thenelevating the other end past the stop rivets 67, 68, as shown in FIG. 6.In the rare instance where liquid has seeped between the sealing rings83 and the pans 61, 62, such a removable arrangement of the heatingpanels is desirable to permit cleaning of the pans 61, 62.

The arrangement of electrical connectors and conductors within the base11 and cover 12 is illustrated in FIG. 4. A male power input plug 90 ismounted interiorally of the base 11 along the back wall 23. An aperture91 is provided through the back wall 23 to provide access to the plug90. A pivotally mounted cover 92 selectively opens or closes theaperture 91. The cover 92 is spring loaded inconventional fashion so asto be held selectively in the open or closed position. When the cover 92is open, the electrical supply cord can be attached to the plug 90, asshown in FIG. 7.

A pair of conductors 93, 94 extend from the male plug 90 beneath the pan61 to the interlock component 51. A pair of conductors 95, 96 connectwith the lower heating element 81 and extend through a gromet 97,positioned in an aperture in the bottom wall of the pan 61, to theinterlock component 51. Similarly, a pair of conductors 98, 99 connectwith the upper heating element 81 and extend through a gromet 100 to theinterlock component 52.

Referring to FIG. 7, the electrical interlock components 51, 52 havethree pairs of mating connectors 101, 102 and 103, 104 and 105, 106which make connection when the base 11 and cover 12 are closed. Theconnector pairs 103, 104 and 105, 106 are positioned more closelytogether than are the connector pairs 101, 102 and 103, 104 to preventthe improper attachment of the interlock by-pass cord 50, as will bedescribed.

ment 81. In similar fashion, the conductor 98 connects one terminal ofthe upper heating element 81 to the connector 102.

The connector pairs 103, 104 and 105, 106 must be brought into registrybefore connection is made between the conductor 94 and either of theheating elements 81. By this arrangement, a safety feature is providedwhich serves to de-energize the heating panels 81 when the cover 12 isopened. The conductor 94 connects with the connector 103. The conductors96, 99 connect the connectors 105, 106 to the lower and upper heatingelements 8 1. A conductor 107 electrically interconnects the connectors104, 106. Accordingly when the base 11 and cover 12 are closed, theconnectors 103, 104, 105, 106 are all electrically coupled to theconductor 94 so as to energize the heating elements 81.

While the appliance 10 is primarily intended for operation inclosed-case fashion to warm food clamped between the heating panels 13,14, it is also occasionally desirable to use one or both of the heatingpanels 13, 14 in open-case fashion to keep dishes of foods warm duringserving. Accordingly, two means of over riding the electrical interlockare shown in FIGS. 8-11.

Where only one of the heating panels is required to be used in open-caseoperation, an interlock over-ride plug 110 is provided for insertioninto the connectors 101, 103, of the interlock component 51. As shown inFIG. 9, the plug is provided with connectors 112, 114, 116 which materespectively with the connectors 101, 103, 105. A conductor 117electrically interconnects the connectors 114, 116 so as to enable thesupply of current through the interlock component 51 to the heatingpanel 13. The connectors 114, 116 are positioned more closely togetherthan are the connectors 112, 114 so the plug 110 cannot be improperlyconnected to the interlock component 51.

Where both of the heating panels 13, 14 are needed for use in open-caseoperation, the interlock over-ride cord 50 is connected betweentheinterlock components 51, 52 as shown in FIG. 10. As illustrated inFIG.- 11, the cord 50 is provided with female and male plugs 119, 120having connectors 121, 122 interconnected by a first conductor 131,connectors 123, 124 interconnected by a second conductor 132, andconnectors 125, 126 interconnected by a third conductor 133. Theconnectors 123, 125 and 124, 126 are positioned more closely togetherthan are the connectors 12], 123 and 122, 124 so that the plugs 119, 120cannot be improperly connected to the interlock components 51, 52. Withthe interlock over-ride cord 50 connected between the components 51, 52,both of the heating panels 13, 14 can be energized in open-caseoperation.

Referring to FIG. 12, a rack structure 130 is shown including aplurality of appliance receiving compartments 131. The rack structure130 not only provides a means for storing a plurality of the foodwarming appliances 10, but also provides a means for energizing theappliances at one of several pre-selected times. By this arrangement, aworkman can insert his own food warming appliance 10 into one of thecompartments 131 and then return to a warm lunch at a pre-selected time.

Referring to FIGS. 13 and 14, the compartments 131 are each providedwith a female electrical plug 132 positioned so as to align with theappliance-carried plug 90. In operation, the workman opens the closure92 to expose the plug 90 and then slides the appliance into one of thecompartments 131 until the plug 90 is received by the plug 132. Thisarrangement obviates such safety problems as might otherwise arise wheremany workmen seek to plug their food warming devices into electricaloutlets with power cords draped one over the other, etc.

A separate selector switch 133 is associated with each of thecompartments 131 so as to selectively connect' the plugs 132 to one ofseveral master-timer switches 134, 135, 136. The timer switches 134,135, 136 are each programmed to energize the appliance 10 at a differenttime so as to have the food positioned therein warmed for differentpre-selected serving times. By way of example, the selector switch 113can be used to select a serving time of either 11:30, 12:00 or 12:30.

The rack structure 130 can be provided with windowed doors (not shown)covering each of the compartments 131 where the rack structure is to bepositioned in a dusty environment. The doors can further be providedwith keyed locks in the manner of a baggage locker so that each employeecan insert his food warming appliance and select a serving time with theassurance that the appliance will not be stolen or disconnected, or theserving time changed in his absence.

As should now be apparent from the foregoing description, food to bewarmed is positioned between the heater panels l3, 14. The base 11 andcover 12 are then closed so as to bring the heater panels 13, 14 intofirm contact with opposite sides of the food. The appliance 10 is thenenergized either by means of the power cord 15 or by positioning theappliance as described in the rack structure 130. The heating panels areenergized so as to attain a temperature not substantially in excessofthe temperature to which the food is to be warmed. This heatingcontinues for a period of time sufficient to warm the food to thedesired temperature.

Throughout the foregoing description the term food has been used broadlyto include unwrapped or unpackaged food, wrapped or packaged food, e.g.,food wrapped in aluminum foil, and trays or containers of food, e.g.,frozen dinners. It will be understood that where the food is wrapped,packaged or containerized, the surrounding packaging material ispreferably characterized by a high heat transfer co-efficient and ispreferably in intimate contact with the food so as to permit theconductive transfer of heat from the panels l3, 14 to the food.

Although the invention has been described in its preferred form with acertain degree of particularity, it is understood that the presentdisclosure of the preferred form has been made only by way of exampleand that numerous changes in the details of construction and thecombination and arrangement of parts may be resorted to withoutdeparting from the spirit and scope o the invention as hereinafterclaimed.

What is claimed is:

1. A device for conductively warming food positioned therein comprising:

a. housing means including a pair of structures relatively movabletoward and away from each other between closed and open positions;

b. compartment defining means carried by said structures defining withinsaid structures an insulated heating compartment which is opened whensaid structures are moved to said open position and closed when saidstructures are moved to said closed position;

c. conductive electrical heating means having first and second opposedpanel portions movable relatively toward and away from each other forengaging opposite sides of such food as is positioned therebetween; and,

d. mounting means mounting said heating means internally of saidstructures such that when said structures are closed, said heating meansis positioned within said heating compartment with said opposed portionsbiased relatively toward each other so as to firmly engage oppositesides of such food as is positioned therein.

2. The appliance of claim 1 wherein said first and second panel portionscomprise first and second electrical resistance heating panels adaptedto be connected to a source of electrical energy.

3. The device of claim 2 whereinsaid compartment defining meanscomprises first and second opposed pans which respectively carry saidfirst and second heating panels therein, each of said pans being carriedby a separate one of said structures.

4. The device of claim 3 wherein said mounting means includes biasingmeans interposed between at least one of said heating panels and itsassociated pan to bias said one heating panel toward the other of saidheating panels.

5. The device of claim 4 wherein said mounting means further includesstop means carried internally of said associated pan to limit themovement of said one heating panel toward said other heating panel.

6. The device of claim 5 wherein said stop means comprises at least apair of projections extending inwardly of said associated pan alongopposite sides thereof so as to engage opposite edges of said oneheating panel, whereby said one heating panel can be removed from saidassociated pan by depressing one of said opposite edges and elevatingthe other of said opposite edges past its associated projection.

7. The device of claim 2 additionally including:

a. first and second electrical interlock components electricallyconnected respectively to said first and second heating panels andmounted within separate ones of said structures;

b. electrical conductor means electrically connected to one of saidinterlock components and adapted to be connected to a source ofelectrical energy;

c. said first and second interlock components carrying conductive meanswhich are brought into registry when said structures are closed forsupplying electrical energy from said conductor means to both of saidheating panels, which are disengaged when said structures are opened soas to interrupt the flow of electrical energy from said conductor meansto both of said heating panels.

8. The device of claim 7 additionally including interlock by-pass meansengageable with at least one of said interlock components when saidstructures are open to permit the energization of at least one of saidheating panels.

9. The device of claim 3 wherein said structures are removably hingedtogether by disengageable hinge portions such that said structures canbe pivoted between said open and closed positions when said hingeportions are in operable engagement, and said structures can bepositioned side by side for open-case operation when said hinge portionsare disengaged.

10. A food warming appliance for conductively warming food positionedtherein, comprising:

a. base and cover structures connected together for relative movementtoward and away from each other between closed and open positions;

b. first and second compartment defining means carried respectively bysaid base and cover structures defining within said structures a heatingcompartment which is opened when said structures are moved to said openposition and closed when said structures are moved to said closedposition;

c. first and second electrical heating panel means carried respectivelywithin said first and second compartment defining means for movementtoward and away from each other as said structures move toward and awayfrom each other; and

d. mounting means supporting said heating means within said compartmentdefining means and biasing said heating means relatively toward eachother such that when said structures are in said closed position, suchfood as is positioned between said first and second heating means isfirmly engaged on opposite sides by said heating means whereby heat maybe transfered to the food by conduction from both of said heating means.

11. The food warming appliance of claim 10 wherein said first and secondcompartment defining means comprises first and opposed pan-like membersthe rims of which are brought substantially into alignment when saidstructures are closed.

12. The food warming appliance of claim 11 wherein sealing rings areprovided around the rim of each of said pan-like members and arearranged so as to be brought into sealing engagement with each otherwhen. said structures are closed.

13. The food warming appliance of claim 10 additionally including firstand second frame means positioned around the periphery of each of saidpan-like members for supporting said pan-like members in spacedrelationship to said structures.

14. The food warming appliance of claim 12 additionally including firstand second frame means positioned around the periphery of each of saidpan-like members for supporting said pan-like members in spacedrelationship to said structures, said sealing rings having portionsinterposed between said frame means and said pan-like members forinsulating said pan-like members from said frame means.

1. A device for conductively warming food positioned therein comprising:a. housing means including a pair of structures relatively movabletoward and away from each other between closed and open positions; b.compartment defining means carried by said structures defining withinsaid structures an insulated heating compartment which is opened whensaid structures are moved to said open position and closed when saidstructures are moved to said closed position; c. conductive electricalheating means having first and second opposed panel portions movablerelatively toward and away from each other foR engaging opposite sidesof such food as is positioned therebetween; and, d. mounting meansmounting said heating means internally of said structures such that whensaid structures are closed, said heating means is positioned within saidheating compartment with said opposed portions biased relatively towardeach other so as to firmly engage opposite sides of such food as ispositioned therein.
 2. The appliance of claim 1 wherein said first andsecond panel portions comprise first and second electrical resistanceheating panels adapted to be connected to a source of electrical energy.3. The device of claim 2 wherein said compartment defining meanscomprises first and second opposed pans which respectively carry saidfirst and second heating panels therein, each of said pans being carriedby a separate one of said structures.
 4. The device of claim 3 whereinsaid mounting means includes biasing means interposed between at leastone of said heating panels and its associated pan to bias said oneheating panel toward the other of said heating panels.
 5. The device ofclaim 4 wherein said mounting means further includes stop means carriedinternally of said associated pan to limit the movement of said oneheating panel toward said other heating panel.
 6. The device of claim 5wherein said stop means comprises at least a pair of projectionsextending inwardly of said associated pan along opposite sides thereofso as to engage opposite edges of said one heating panel, whereby saidone heating panel can be removed from said associated pan by depressingone of said opposite edges and elevating the other of said oppositeedges past its associated projection.
 7. The device of claim 2additionally including: a. first and second electrical interlockcomponents electrically connected respectively to said first and secondheating panels and mounted within separate ones of said structures; b.electrical conductor means electrically connected to one of saidinterlock components and adapted to be connected to a source ofelectrical energy; c. said first and second interlock componentscarrying conductive means which are brought into registry when saidstructures are closed for supplying electrical energy from saidconductor means to both of said heating panels, which are disengagedwhen said structures are opened so as to interrupt the flow ofelectrical energy from said conductor means to both of said heatingpanels.
 8. The device of claim 7 additionally including interlockby-pass means engageable with at least one of said interlock componentswhen said structures are open to permit the energization of at least oneof said heating panels.
 9. The device of claim 3 wherein said structuresare removably hinged together by disengageable hinge portions such thatsaid structures can be pivoted between said open and closed positionswhen said hinge portions are in operable engagement, and said structurescan be positioned side by side for open-case operation when said hingeportions are disengaged.
 10. A food warming appliance for conductivelywarming food positioned therein, comprising: a. base and coverstructures connected together for relative movement toward and away fromeach other between closed and open positions; b. first and secondcompartment defining means carried respectively by said base and coverstructures defining within said structures a heating compartment whichis opened when said structures are moved to said open position andclosed when said structures are moved to said closed position; c. firstand second electrical heating panel means carried respectively withinsaid first and second compartment defining means for movement toward andaway from each other as said structures move toward and away from eachother; and d. mounting means supporting said heating means within saidcompartment defining means and biasing said heating means relativelytoward each other such that when said structures are in said closeDposition, such food as is positioned between said first and secondheating means is firmly engaged on opposite sides by said heating meanswhereby heat may be transfered to the food by conduction from both ofsaid heating means.
 11. The food warming appliance of claim 10 whereinsaid first and second compartment defining means comprises first andopposed pan-like members the rims of which are brought substantiallyinto alignment when said structures are closed.
 12. The food warmingappliance of claim 11 wherein sealing rings are provided around the rimof each of said pan-like members and are arranged so as to be broughtinto sealing engagement with each other when said structures are closed.13. The food warming appliance of claim 10 additionally including firstand second frame means positioned around the periphery of each of saidpan-like members for supporting said pan-like members in spacedrelationship to said structures.
 14. The food warming appliance of claim12 additionally including first and second frame means positioned aroundthe periphery of each of said pan-like members for supporting saidpan-like members in spaced relationship to said structures, said sealingrings having portions interposed between said frame means and saidpan-like members for insulating said pan-like members from said framemeans.